The invention relates to magnetoresistive sensors for angle measurements. A preferred field of application of magnetoresistive sensors is their use for contactless angle measurement.
Magnetoresistive sensors for angle measurements such as, for example, the sensors of the type KMZ 41, manufactured and marketed by Philips Semiconductors, are principally known and utilize the magnetoresistive effect. A preferred use of MR sensors is in the weak field, angle and rotation measurements and in Magnetic Force Microscopy measurements (abbreviated MFM measurements; for example, on crystals of the product marketed as KMZB34 by Philips Semiconductors).
Magnetoresistive sensors (also abbreviated to and known as MR sensors) for angle measurements operate in the saturation range, i.e. they utilize the effect that a sufficiently strong external magnetic field H rotates an internal magnetization M of the sensor elements in the arrangement of the magnetoresistive sensor in a (substantially) fully parallel direction. In the case of said sensor KMZ 41, the magnetic field strength of the external magnetic field required for full alignment of the internal magnetization is 70 to 100 kA/m. The generation of such a strong magnetic field requires a relatively high number of constructive components. A reduction of this high field strength is desirable.
It is an object of the invention to achieve a decrease of the magnetic field strength required for saturation (parallel setting).
This object is solved by a magnetic field-sensitive sensor arrangement comprising at least a sensor element of NiFe material arranged substantially in a plane and being substantially strip-shaped in this plane, which sensor element has a contour in this plane which comprises substantially a central area with mutually parallel boundary lines, and, at least at one of the ends of the central area, an end segment which is at least substantially bounded by elliptical curves and/or is tapered towards the end.
Advantageous embodiments of the invention are defined in the dependent claims.
The magnetic field-sensitive sensor arrangement according to the invention is thus distinguished by shape-optimized, strip-shaped thin layers of a magneto-resistive material, preferably permalloy or NiFe 81:19.
The desirable decrease of said high field strengths can be achieved by increasing the tendency of the internal magnetization to change its direction. An increase of the tendency of the internal magnetization to change its alignment is achieved, according to the invention, by strip-shaped sensor elements of NiFe material having elliptical contours or tapered ends.
The rotatability of the magnetization is enhanced in the magnetic field-sensitive sensor arrangement according to the invention by giving the MR sensor elements a suitable shape.
A circular MR structure provides the principally easiest rotatability of the magnetization. It is therefore obvious to realize the sensor elements also in a circular shape. However, this has the drawback thatxe2x80x94conditioned by manufacturing spreads (mask adjustment in photolithography, etc.)xe2x80x94such circular structures can only be contacted incompletely, i.e. with high tolerances, and, moreover, require a large surface area.
The invention is based on the recognition that MR structures utilizing elliptical and circular geometries in a defined way have a far better rotatability of the magnetization than the typically used rectangular structures. In this respect it is important that elliptical structures with pointed corners have a very weak domain splitting. By combination with rectangular parts of the MR strips, these structures can nevertheless be manufactured in a satisfactorily reproducible way while maintaining typical manufacturing tolerances.
The invention has the advantage of a reduction, which is comparably easy to realize, of the required saturation field strength to 20-30 kA/m at a small angle error by shape anisotropy. The reduction of the saturation field strength is supported by using very thin layers, while the reduction of the shape anisotropy is achieved by the shape optimization of the strips according to the invention.